As a process of producing HCFC-124 and HFC-125, a process has been known in which perchloroethylene (which is hereinafter also referred to as "PCE") is reacted with an excessive amount of hydrogen fluoride (which is hereinafter also referred to as "HF") in a vapor phase to form 1,1-dichloro-2,2,2-trifluoroethane (which is hereinafter also referred to as "HCFC-123"), HCFC-124 and HFC-125 (see International Publication No. WO 92/16479). The Publication discloses that HCFC-123, HCFC-124 and HCFC-125 are formed at a HF/PCE molar ratio between about 3/1 and 10/1, a reaction temperature between 250.degree. C. and 450.degree. C., and a reaction contact period between 0.1 sec. and 60 sec. using a metal such as zinc and/or chromium supported on alumina and/or aluminum fluoride as vapor phase reaction catalyst.
The inventors have found that when such a process is carried out, the following problems occur due to a large amount of generated reaction heat: difficult reaction control, remarkable degradation of catalyst performance, and formation of a relatively large amount of by-products. The reaction which produces HFC-125 by reacting PCE and HF is an exothermic reaction of which heat of reaction is so large as about 28 kcal/mol. Thus, when the reaction is carried out in a vapor phase, a hot spot is formed in a reactor so that reaction temperature control may become difficult, and a large amount of by-products may be sometimes formed due to the temperature increase, which reduces a yield of an objective product. One manner which overcomes these problems uses a multi-tubular reactor for the reactor. However, this manner requires an expensive facilities cost, which becomes another problem. Another manner overcoming the problems increases a large molar ratio of HF/PCE and uses unreacted PCE as a diluent so as to stably control the temperature. In this manner, an amount of a starting material stream which flows through the reaction process is increased, so that a scale of a reaction facilities becomes large, which is also another problem.
Thus, it has been desired to provide a process which overcomes the above problems and which effectively produces HFC-125 and/or HCFC-124 in a commercial scale at an inexpensive cost.
It is to be noted that the above International Publication discloses only the vapor phase reaction as described above, and does not disclose the catalyst degradation, a manner of prevention of the catalyst degradation, a control manner of generated reaction heat, a separation process of reaction mixture comprising products and by-products, recirculation of unreacted HF, or recirculation of HCFC-123, HCFC-124 and so on for purpose of the production of HFC-125, which is explained in the detail below in the present description.
Although each of a process for the production of HCFC-123 through a liquid phase reaction using PCE as a starting material, and a process for the production of HCFC-124 and/or HFC-125 through a vapor phase reaction using HCFC-123 as a starting material is known individually as explained below, no profit obtained by combining these process has been known, and the profit is firstly provided by the present invention.
As a production process of 1,1,2-trichloro-2,2-difluoroethane (which is hereinafter also referred to as "HCFC-122") and HCFC-123, a process has been known in which PCE and HF are reacted in a liquid phase to form 1,1,2,2-tetrachlorofluoroethane (which is hereinafter also referred to as "HCFC-121"), HCFC-122 and HCFC-123 (see U.S. Pat. No. 4,258,225). The patent discloses tantalum fluoride (TaF.sub.5) or niobium fluoride (NbF.sub.5) as catalyst used in the liquid phase reaction. As in the case of the above International Publication, a withdrawal process of reaction products from the reaction process, a separation process of the reaction mixture, a recirculating process of the reaction mixture or the like, which is disclosed by the present description.
A process for the production of HCFC-124 and HFC-125 from HCFC-123 as a starting material has been known in which HCFC-124 and HFC-125 are formed by reacting HCFC-123 with an excessive amount of HF in a vapor phase (see International Publication No. WO 92/16482). The Publication discloses that HCFC-124 and HCFC-125 are formed at a HF/HCFC-123 molar ratio between about 2/1 and 10/1, a reaction temperature between 225.degree. C. and 450.degree. C., and a reaction contact period between 0.1 sec. and 60 sec. using a metal such as zinc and/or chromium supported on alumina and/or aluminum fluoride as vapor phase reaction catalyst. As in the case of the above International Publication, this Publication does not disclose a separation process of the reaction mixture comprising the products and the by-products or recirculation of unreacted HF, HCFC-123 and so on, which is disclosed by the present description. In addition, no production process is disclosed which produces HCFC-123 as a starting material.
By the way, as to separation of HF and organic materials relating to the present invention from a mixture comprising those materials, for example a process has been known in which a mixture of HCFC-123, HCFC-124 and HF is cooled to cause liquid phase separation (i.e. separation into insoluble liquid phases) so that the mixture is separated into a liquid phase which is composed mainly of HF and another liquid phase which is composed mainly of HCFC-123 and HCFC-124 (see European Patent Publication (EP-B) No. 353970). The Publication discloses further separation of each of HF, HCFC-123 and HCFC-124 by means of distillation after the liquid phase separation.